John L. Monteith

Bio: John L. Monteith is an academic researcher from International Crops Research Institute for the Semi-Arid Tropics. The author has contributed to research in topics: Atmosphere & Transpiration. The author has an hindex of 58, co-authored 138 publications receiving 30024 citations. Previous affiliations of John L. Monteith include Goddard Space Flight Center & University of Nottingham.

The carbon-dioxide flux over a field of sugar beet

Abstract: The difference of CO2 concentration at two heights above a sugar beet crop was measured with a sensitive infra-red gas analyser. The ratio of evaporation to humidity gradient and of total heat flux to wet-bulb temperature gradient gave a transport number for calculating CO2 flux, assumed proportional to CO2 gradient and wind speed. In August and September 1958 there was often a constant upward flux at night (mean 0·05 mg cm−2 hr−1) attributed to respiration by plants and soil micro-organisms; but during daylight, photosynthesis gave a downward flux varying with solar radiation and reaching a maximum of 0·4 mg cm−2 hr−1. From 31 July to 11 September the net downward flux of atmospheric CO2 was 158 ± 29 mg cm−2 compared with an uptake of 217 ± 38 mg cm−2 estimated from dry matter increase of sampled plants. During October there was a net upward flux of 4·9 mg cm−2 day−1 attributed to a striking increase in amount of CO2 produced in the soil.

Attenuation of solar radiation: A climatological study

Abstract: Daily totals of direct and diffuse radiation transmitted by a cloudless atmosphere are calculated from the absorption and scattering coefficients given by Houghton (1954). Estimates of total (direct plus diffuse) radiation (T1) agree well with extreme maxima recorded at several British stations, but during spells of cloudless summer weather in south-east England attenuation by aerosol decreases total radiation on average by 10 per cent, and increases the ratio of diffuse to total radiation by about 8 per cent of T1. The ratio of mean monthly radiation at country stations T2 to estimated T1 can be expressed as a function of cloud reflection (ρ), cloud absorption (ϕ), and surface reflection (α); and the values ρ = 0·50, ϕ = 0·16 are consistent with surface and aerial measurements. With α = 0·20, T2/T1 is approximately (1−0·61c) (0·6 < c < 0·9) where c is fractional cloudiness. The diffuse component beneath cloud can be estimated separately. Absorption by man-made aerosol reaches maxima of 26 per cent at Kew and 30 per cent at Kingsway in January, and varies seasonally with measured smoke. In the country, absorption by pollution is negligible in summer but may reach 5 to 10 per cent in winter. At Kew, absorption by cloud and total back-scattering (local planetary albedo) are about 9 per cent and 41 per cent of extra-terrestrial flux respectively, with little seasonal variation.

Windspeed dependence of heat and mass transfer through coats and clothing

Abstract: Penetration of a layer of fibre by wind reduces its effectiveness as a barrier to heat flow. In the literature, the dependence of coat or clothing insulation I(u) on windspeed u is usually described by a relation of the form I(u) = I(0) − au1/2, where a is a constant. Re-analysis reveals that it is more appropriate to treat coat conductance (proportional to 1/I) as a linear function of windspeed. Vapour conductance can also be treated as a linear function of windspeed.

A thermocouple method for measuring relative humidity in the range 95-100%

Abstract: At high relative humidities a current of 30 mA through a 38 s.w.g. chromel-p/constantan thermocouple produces sufficient Peltier cooling to form a film of water on the junction which may then be used as the wet-bulb of a psychrometer. The wet-bulb depression can be read to 0.001° C and in the range 97-100% changes of 0.01% relative humidity can be detected. After calibration over sodium chloride solutions the psychrometer has been used to determine the water content/free energy curves of two soils, and good agreement has been obtained with previous determinations by other methods.

Crop evapotranspiration : guidelines for computing crop water requirements

Abstract: (First edition: 1998, this reprint: 2004). This publication presents an updated procedure for calculating reference and crop evapotranspiration from meteorological data and crop coefficients. The procedure, first presented in FAO Irrigation and Drainage Paper No. 24, Crop water requirements, in 1977, allows estimation of the amount of water used by a crop, taking into account the effect of the climate and the crop characteristics. The publication incorporates advances in research and more accurate procedures for determining crop water use as recommended by a panel of high-level experts organised by FAO in May 1990. The first part of the guidelines includes procedures for determining reference crop evapotranspiration according to the FAO Penman-Monteith method. These are followed by updated procedures for estimating the evapotranspiration of different crops for different growth stages and ecological conditions.

Large Area Hydrologic Modeling and Assessment Part i: Model Development

Abstract: A conceptual, continuous time model called SWAT (Soil and Water Assessment Tool) was developed to assist water resource managers in assessing the impact of management on water supplies and nonpoint source pollution in watersheds and large river basins. The model is currently being utilized in several large area projects by EPA, NOAA, NRCS and others to estimate the off-site impacts of climate and management on water use, nonpoint source loadings, and pesticide contamination. Model development, operation, limitations, and assumptions are discussed and components of the model are described. In Part II, a GIS input/output interface is presented along with model validation on three basins within the Upper Trinity basin in Texas.

Primary Production of the Biosphere: Integrating Terrestrial and Oceanic Components

Abstract: Integrating conceptually similar models of the growth of marine and terrestrial primary producers yielded an estimated global net primary production (NPP) of 104.9 petagrams of carbon per year, with roughly equal contributions from land and oceans. Approaches based on satellite indices of absorbed solar radiation indicate marked heterogeneity in NPP for both land and oceans, reflecting the influence of physical and ecological processes. The spatial and temporal distributions of ocean NPP are consistent with primary limitation by light, nutrients, and temperature. On land, water limitation imposes additional constraints. On land and ocean, progressive changes in NPP can result in altered carbon storage, although contrasts in mechanisms of carbon storage and rates of organic matter turnover result in a range of relations between carbon storage and changes in NPP.

Correction of flux measurements for density effects due to heat and water vapour transfer

Abstract: When the atmospheric turbulent flux of a minor constituent such as CO2 (or of water vapour as a special case) is measured by either the eddy covariance or the mean gradient technique, account may need to be taken of variations of the constituent's density due to the presence of a flux of heat and/or water vapour. In this paper the basic relationships are discussed in the context of vertical transfer in the lower atmosphere, and the required corrections to the measured flux are derived. If the measurement involves sensing of the fluctuations or mean gradient of the constituent's mixing ratio relative to the dry air component, then no correction is required; while with sensing of the constituent's specific mass content relative to the total moist air, a correction arising from the water vapour flux only is required. Correspondingly, if in mean gradient measurements the constituent's density is measured in air from different heights which has been pre-dried and brought to a common temperature, then again no correction is required; while if the original (moist) air itself is brought to a common temperature, then only a correction arising from the water vapour flux is required. If the constituent's density fluctuations or mean gradients are measured directly in the air in situ, then corrections arising from both heat and water vapour fluxes are required. These corrections will often be very important. That due to the heat flux is about five times as great as that due to an equal latent heat (water vapour) flux. In CO2 flux measurements the magnitude of the correction will commonly exceed that of the flux itself. The correction to measurements of water vapour flux will often be only a few per cent but will sometimes exceed 10 per cent.